Conventional portable digital imagers, such as clip-on thermal imagers (COTIs), are designed for use in either a handheld mode or an attached mode (such as when attached to night-vision goggles (NVG)), but not both. When a portable digital imager is attached to a device such as an NVG (hereinafter referred to as the mounted mode), the optical eyepiece or digital display that presents an image to the user is typically positioned too far from the eye to enable the user to easily use the device in the handheld mode, especially when the user is wearing eyeglasses or ballistic goggles. This limits the flexibility of conventional portable digital imagers and requires users who may need to use an imager in both the mounted and handheld modes to carry multiple devices.
In addition, conventional portable digital imagers are typically optimized for use in either the handheld or mounted mode. For example, owing to different distances of the display from the user's eye, the user might prefer different display brightnesses depending on whether the digital imager is mounted or handheld. A user who attempts to use an imager in both modes might therefore need to manually adjust system settings such as brightness when changing modes. Moreover, while manually adjusting the system settings, the user is unable to use the digital imager for visual augmentation, and can therefore fail to detect relevant objects during this adjustment period.
Furthermore, conventional digital imagers that use optical eyepieces are designed to use either inverting or non-inverting eyepieces, but not both. The user of a conventional digital imager who wishes to replace a heavier and bulkier non-inverting eyepiece with a lighter and smaller inverting eyepiece must also replace the digital imager with one that digitally inverts the image.
Therefore, there is a need for an eyepiece that can enable a portable digital imager, to which the eyepiece can be easily attached and from which it can be easily detached, to be used in both mounted and handheld modes.